Conventionally in the research on the magnetic-confinement fusion, in order to observe the state of core plasma, shooting pellets containing a tracer material into a flow of plasma is carried out.
The pellets consist of a spherical central part containing the tracer material and an outer layer covering its circumference. When the pellets are shot into the plasma, the pellets move to the center of the flow of plasma while the outer layer is being peeled off by the energy of the plasma. When the outer layer is peeled off and the central part is exposed, since the tracer substance emits light by the energy of the plasma, by tracing the light emission, the information on the flow and the like of the plasma can be acquired.
Such pellets are manufactured conventionally by making a hole on a sphere constituted of a resin or the like, filling the sphere with a tracer material separately weighed, and refilling in the hole (for example, see Non Patent Literature 1).